Concentration of phosphate minerals



Patented Feb. 15, 1949 fritfrlazir'rn."` orifice CONCENTRATION F PHOSPHATE MINERALS James B. Duke, Lakeland, Fla., assignor to Minerals Separation North American Corporation. New York. N. Y., a corporation of Maryland Application-November 1i, 1945, Serial No. 628.585

The present invention relatesto concentratio of phosphate minerals fron their ores, and may 1 be regarded as an improvement upon the method covered by the patent to Arthur Crago No. 2,293,640, issued August 18, 1942, now owned by the assignee of the present application.

That Crago ypatent describes and claims a method of concentrating phosphate minerals from their ores, which comprises subjecting the ore in an aqueous pulp to a concentrating operation with reagents to separate a rougher concentrate of the phosphate values admixed with entrained siliceous sangue, treating the rougher` concentrate with: a mineral acid to remove the effect of the reagents used in its production, and thereafter subjecting the rougher concentrate in an aqueous pulp to a concentrating operation A to separatea collected material largely composed of the entrained siliceous gangue, thereby produ'cing a nal phosphate concentrate.

The reagents, described in the Crago patentv as useful in the rst step of that method. are such negative-ion agents as the higher fatty acids, such as sh-oil fatty acid and oleic acid and their soaps, the resinacids and their soaps, wood lay-products fatty acids, naphtheinicv acids and their salts, the higher sulpho-fatty acids and their salts 'with the proper bases. the acid esters of high-molecular-weight aliphatic alcohols with inorganic acids and their alkali-metal and alkaline-earth-metal salts, the higher xanthates,

etc. The reagents described as useful in the last step of that method are of the positive-ion type such as the higher aliphatic amines and their salts with water-soluble acids. the esters of amino-alcohols with high-molecular-weight l fatty acids and their salts with water-soluble acids, the higher alkyl-O-substituted isoureas and their salts with water-soluble acids. the resin amines. and their salts with water-soluble acids, the higher aliphatic quaternaryl ammonium bases and their salts with water-soluble acids, the higher alkyl pyridinium salts of watersoluble acids. the higher alkyl quinolinium salts of water-soluble acids. etc; It is also stated in that patent that the use of ananionic active fatty acid compound is preferred in the carrying out of the iirst concentratingv operation, while the vuse of a cationic-active amine compound is preferred in the carrying out of the second concentrating operation. In performing the intermediate stepbetween the two concentrating operations. the mineral acid employed is described in that patent as preferably sulfuric acid because of its low cost. These various re- 'i claim.v (o1. zoe-1ct) present invention. l

The Crago patent also states that in the carrying out of the concentrating operations used in 5. practicing the method of that patent. any concentrating 'device may be used which is capable of discharging the collected material ,in such forms as floating froth, skin or surface filoat. individual agglomerates.- etc.; and' that such delo concentrating tables, the collected material being discharged in the case of the former in the form oi a iioating froth over the lip of the machine, and in the case of the latter in the l5 at the table side. Such devices may be used in 'practicing the improved method of the present invention.

In the commercial 2o the Cragol patent it sometimes occurs that, while the final phosphate concentrate produced is of high grade, the percentage of the available phosphate in the feed which appears in the nal phosphate concentrate is not as high as desired. That is, although aphosphate concentrate of high grade is obtained, a considerable percentage of the phosphate in the feed has been collected with the siliceous gangue and sent to waste in the last step of the process.

Dimculty in obtaining recovery :in the unal phosphate concentrate of a satisfactory per-.- centage of the phosphate in the feed,- as above mentioned, seems to be due to a number of causes which are more likely to occur in plant opera.`=` tion than in laboratory practicing of the method of said Crago patent. My belief is that when the unsatisfactory percentage of recovery just mentioned is encountered it is due to failure adequately to treat the rougherl concentrate with a mineral acid to remove the eect of the reagents used in'1 its production. v In a plant operation, that failure may bel due to the use of insumcient mineral acid or to lack of adequate mixing of the acid with the rougher concentrate or to both, or to other reasons. Various attempts have been made to insure a high percentage of phosphate recovery in practicing the method of the Crago patent, but these attempts have either been more'or less unsuccessful or have required the use of additional reagents or apparatus or both, which has increased the cost vand complexity of the plant and its operation.

.The general object of the present invention is to make more certain a high percentage recovery of phosphate in the iinal phosphate concentrate vices include iotation machines and gravity .form of skin float and suspended agglomerates practice of the process oi produced by the method of said Crago patent.

According to the present invention. the desired end is achieved, with economy in the use of reagents and without substantial increase in the apparatus employed in the plant, by subjecting the acid-treated rougher phosphate concentrate to treatment resulting in the removal therefrom of a, high-grade concentrate of the phosphate values; whereupon the residue of that treatment is subjected in an aqueous pulp to a concentrating operation (according to the last step of the method of the Crago patent) to remove a coilected material largely composed of siliceous gangue which is sent to waste: after which the residue from the last mentioned operation and the phosphate concentrate resulting from the first mentioned operation are combined to produce the nal high-grade concentrate containing a high proportion of the phosphate in the ore. In practicing the improved process, I have discovered that, prior to subjecting the acid-treated rougher phosphate concentrate to treatment to remove therefrom a phosphate concentrate, treatment with an inert oil such as kerosene or pine oil or both is advantageous. While kerosene seems to be preferable as the inert oil, other hydrocarbon oils such as light gravity petroleum oils may be employed. When pine oil is used, it acts Iboth as a frothing agent and as an inert oil in the treatment. The amount of thephosphate concentrate lobtained by this concentrating operation, following the acid treatment of the rougher phosphate concentrate, is of course relatively small, but this concentrate is of high grade; and the removal of this lphosphate concentrate from the material that is the feed to the last step of the method of the Crago patent, substantially prevents phosphate from being separated from that feed along with the siliceous gangue which is sent to waste.

An important advantage of the present invention is that it requires the use of only small amounts of reagents and calls for vvery little additional plant equipment. For example, in plants where the nal operation of the method of the Crago patent had been performed in a bank of flotation cells, the inert oil or oils may be introduced into the feed to the first of those cells, and the froth-floated` phosphate concentrate from that cell may be removed; the positive-ion reagents are introduced into the machine discharge from that rst cell which is fed to the remaining cells from which froth-floated siliceous gangue is removed and sent to waste: after which the froth-floated phosphate concentrate from the first cell and the machine discharge of the other cells are combined to form the final phosphate concentrate.

The method of the present invention will be understood from the following description, taken in connection with the accompanying drawing which shows a flow-sheet oi a typical plant practicing the method. It will be understood that this flow-sheet is merely an aid to the understanding of the invention, and that various modifications in the appartus referred to in the flow-sheet may be resorted to without departing from the spirit ofthe invention as defined in the claims hereto appended.

Referring to the flow-sheet shown in the drawing. it will be evident that the four steps of the improved method are separated by dash lines. The first stepA results in obtaining, from the raw phosphate feed to the plant, of a rougher phosphate concentrate; the second step involves the acid-treating of that rougher phosphate concentrate thereby obtaining an acid-treated rougher phosphate concentrate, according to the teachings of the said Crago patent; the third (new) step involves the treating of said acid-treated rougher phosphate concentrate with inert oils and the removal of a phosphate concentrate which is apart of the final phosphate concentrate: and the.` fourth step involves the treating of the machine discharge from the third step with a positive-ion reagent, followed by flotation treatment which eliminates a siliceous froth product which is sent to waste; leaving the machine discharge as a phosphate concentrate which is combined with the phosphate concentrate produced in the third step, to give the final phosphate concentrate.

The invention and the advantages thereof will fbe understood from consideration of tests which will nowv be described. Test 1 shows the results from use of the invention, when the acid-treating of the rougher phosphate concentrate-in the second step oi the method is inadequate to remove the effect of the reagents used in the production of theirougher phosphate concentrate. Test 2 shows the results when, in practicing the invention, the acid-treating of the rougher phosphate concentrate in the second step is more nearly adequate to remove the effect of the reagents used in the production of the rougher phosphate concentrata( Test 3 shows the results of practicing the invention, when the acid treatment of the second step is stili more nearly adequate to remove the efiect of the reagents used in the production of the rougher phosphate concentrate. In carrying out these tests, the adequacy of the acid treating step was increased from Test No. 1 to Test No.2 to Test No. 3, by increasing the amount of mineral acid used; but it is to be understood that in plant operation the adequacy of the acidtreating step may dependy on'other factors than the amount of acid used, for example, the thoroughness with which the acid is mixed with the rougher phosphate concentrate in the acid agitator, and by other factors. For the purpose of explaining and demonstrating the advantages of the present invention, varying the amount of mineral acid employed to remove the effect of the reagents used in the 'production ofthe rougher phosphate concentrate is a simple method for varying the adequacy of the acid treatment of the rougher phosphate concentrate.

In each of the three tests hereinafter de scribed, the feed was obtained from deslimed. minus 14-mesh, phosphate ore which was screened on a 35-mesh screen so as to obtain the minus 35-mesh fraction of the ore which was used as the feed. In each of the tests, this feed, which contained about 35.7% B. P. L. (bone phosphate of lime), was conditioned at about 70% solids with 0.5 1b. caustic soda, 4.4 lbs. fuel oil and 1.1 lbs. tall oil fatty acid, per ton of solids, for about two minutes. ditioned feed was subjected to froth-flotation treatment resulting in the production in a frothfloat of a rougher phosphate concentrate, the

silicous machine discharge being' sent to waste. The rougher phosphate concentrate so obtained was dewatered to approximately 50% solids and then agitated for about two minutes with sulfuric acid, after which the solids were washed substantially free from slimes, reagents and acid; the amount of sulfuric acid used being 1.0 ib., 2.0 lbs. and 4.0lbs. in Tests Nos. 1, 2 and 3, respectiveiy. The washed, acid-treated, rougher Then this conallurglcal results of Tests 1, 2

aliene@ phosphate concentrate thusobtained was then made into a thin plup at about 10% solids, `and fed to a froth-flotation cell in which it was conditiohed for about 15 seconds with,1.8 lbs. kerocentrate oi' high grade with a recovery of a high percentage of the phosphate in the original feed. It will be noted that the conditions in Tests 1, 2 and 3 were the same, except that the amount oi.' sulfuric acidj employed was 1.0 lb., 2.0 lbs. and `4.0 lbs. in the respective tests. The interesting metand ysare shown in thefollowing tables:

Testa' 1 Phosphate concentrate (froth product) obtained after treatment with. inert oils- 3rd step 'rest we. n. P. I.. v na. Pkg-c? Per een! Per om! Per cent Per cent l 15. 5 76.3 4. d 82. 9 l. 2 75. 8 4. 9 2. 5 0. 2 72. l 9. 3 0. 3

TAsLl 2 Phosphateconcentra (machine discharge) obtained after treatment with apositivefion reagents-4th. .step f 'mi 3.11.1.. ms.

Per cent Per :est Per cent che* .gis

- Tests 3 Final phosphate concentrate-combined concentrates obtained byrd and 4th steps Y B. P. L Test Vi t. B. P. Ins. Rec

Per een! Per een! Per cen! Per cent l 43. 77. 9 2. 8 93. 3 2 42. 8 78. 7 2. 1 04. 6 3 42.4 80.0 l. 5 94. 2

From consideration of the foregoing tables, it will be evident that each of thethree tests produced a vfinal phosphate concentrate of high grade B. P. L.) with high recovery y(% B. P. L. Rec), in spite of the wide differences in the adequacy of lthe treatment with acid to remove the effect of the reagents used in the production of the rougher phosphate concentrate.

Test 1 illustrates the usefulness of the invention when the eil'ects ci' the reagents used in obtaining the rougher phosphate concentrate have been far from eliminated by the use of only 1.0 lb. sulfuric acid.l As shown in Table 1.

the phosphate concentrate (froth product) obof the weight of the original feed, Aand had a v grade of 76.3% B. P. L. with B. P. L. recovery of 82.9%.A As shown in Table 2, the phosphate concentrate (machine discharge) obtained after treatment with positive-ion reagents, was 27.5% of the weight of the original ieed,.and had a grade of '79.0% B. P. L. witha B. P. L. recovery of only 60.4%. Nevertheless, as shown in Table 3, the final phosphate concentrate was 43.0%V of the .weight of the original feed. and had a grade ci' 77.9% B. P. L. with B. P. L. recovery oi 93.3%. v'li'est 2 illustrates the usefulness of the inven- I Vtion when the effects of the reagents used in obtaining the rougher concentrate have been largely eliminated, as would be customaryin a plantpracticing the invention, by the use of 2.0 lbs. sulfuric acid. In thisv case, as shown in Table ifthe phosphate concentrate (froth product) obtained after treatment with inert oils had a grade oi' 76.8% B. P. L. (nearly as high as the correspondinggrade in Test l), but was only 1.2% of the weight of the original feed, with B. P. L. reco'very of only 2.5%. Also, it will be noted that in Test 2, as shown in Table 2, the phosphate concentrate (machine discharge) obtained after treatment with positive-ion agents, was 41.6% of the weight of the original feed with 92.1% B. P. L. recovery,

' both oit-which results were far better than in Test 1. Moreover, as will be evident from Table 3, the hnal phosphate concentrate obtained by Test 2 had somewhatbetter metallurgical characteristics than in Test 1. Test 2 may be regarded as a good example of the practice ofthe method of the present invention, with economy in the use of reagents.

Test 3 is included merely for the purpose of I demonstrating the correctness of the theories advanced in this specification. including the observation that in practicing the method ofthe Crago B. P. L..

Rec.

patent; failure to obtain high B. P. L. recovery is due 'to not sumciently eliminating the eiiects of the reagents used in obtaining the rougher concentrate. In this test. the extravagant use of 4.0 lbs. sulfuric acid evidently almost completely eliminated those effects. Under these circumstances, it will be noted from Table 1 that the phosphate concentrate (froth product) obtained after treatment with inert o ils was so insignificant in weight and so low in B. P. L. recoveryv that in this case the third step of the method had but little eiect upon the final phosphate concentrate described in Table, 3'.

` Thus, the results of Tests 1, 2 and 34 prove the' usefulness in plant operation of the third step in In practicing themethod of the Crago patent,

I it is' customary in some cases to subject 'the rougher'phosphate concentrate produced by the rst step to a cleaning operation before subjecting it to the acid treatment. In the tests hereinbefore described, this cleaning. operation was not used, but of course it is to be understood that such a cleaning operation may be used in the present method without departing from the spirit assauts oi' the invention. and that in the following claims the expression rougher concentrate of the phosphatevalues mixed with silicious sangue" is 1n.. tended to refer to the product resulting from the mst step oi the method, whether or not that product is subjected to a cleaning operation prior to the acid treatment of it. i

What is claimed is:

1. A method of concentrating phosphate minerals from their ores, which comprises subjecting the ore in an aqueous pulp to a concentrating operation with negative-ion reagents to separate a rougher floating concentrate of the phosphate values mixed with silicious gangue, conditioning an aqueous pulp of that rougher phosphate concentrate with a mineral acidand then dewatering' said pulp thereby eliminating a large part of. said mineral acid and also the agents used in the production of that rougher phosphate concentrate,

adding .an inert oil to an aqueousfpulp o f that acid-treated rougher phosphate concentrate andi.

subjecting said pulp to a concentrating operation resulting in the removal and saving of a highgrade floating concentrate of a part of the phosphate values, subjecting the residue of that operation in an aqueous pulp to a concentrating operation with added positive-ion reagents to remove and discard a floated material largely composed of silicious gangue, and combining the residue from that operation with the previously mentioned high-grade phosphate concentrate, thereby producing a nal high-grade phosphate concentrate containing a high proportion of the phosphate in the ore.

2. A method of concentrating phosphate minerals from their ores, which comprises subjecting the ore in an aqueous pulp to a, concentrating operation with negative-ion reagents to separate a rougher iloating concentrate of the phosphate values mixed with silicious gangue, conditioning an aqueous pulp of that rougher phosphate concentrate with a mineral acid and then dewatering 'me pulp snc washing n with wam thereby eliminating substantially all oi said mineral acid and the azents used in the production oi that rougher phosphate concentrate. adding an inert oil to anaqueous pulp oi' that acid-treated and washed rougher phosphate concentrate and subjecting it to a concentrating operation resulting in the removal and saving ot a high-grade oating concentrate of a part oi the phosphate values, subjecting the residue of that operation in an aqueous pulp to a concentrating operation with added positive-ion reagents to remove and discard a floated material largely composed of silicious genaue, and combining the residue Vfrom the insert oil is pine oil.

7. A method according to claim 1, in which ttiile inert oil is a mixture of kerosene and pine o JAMES B. DUKE.

REFERENCES CITED .The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,175,724 Gaudin Apr. 2, 1940 2,293,640 Crago Aug. 18, 1942 2,389,727 Herkenhoii Nov. 27, 1945 

